This invention relates to angioplasty perfusion catheters with a perfusion channel, comprising a dilatation balloon and a perfusion tunnel through the balloon.
Catheters of that kind, such as the perfusion catheter described in U.S. Pat. No. 4,581,017, permit the insertion of the depressurized balloon into a stenosis; the balloon may then by expanded by means of a suitable fluid supply feeding the inflating tube in order to compress the stenosis radially outward; as the perfusion catheter has a side orifice located before the balloon, the blood may flow through the perfusion catheter past the balloon and the stenosis to exit through a central outlet at the distal end of the perfusion catheter, which maintains continuity of blood flow in the blood vessel, and which obviates the necessity of removing the catheter from a stenotic artery every five-ten seconds in order to avoid heart damage due to lack of blood flow. Inflation times longer than five-ten seconds become necessary when, due to the dilatation by the balloon, flaps have been formed in the vessel, and these flaps threaten to obstruct the vessel. Therefore, the dilatation balloon must be inflated repeatedly in the position of the stenosis in order to support the flaps and press them back to the vessel wall where they heal and bind again to the vessel wall. Sometimes, this process is finished in a very short time; but often, this favourable short healing is still too long to allow complete cutting of the blood flow during that time. That is the occasion where perfusion balloon catheters are needed because they allow extension of the inflation time without endangering blood supply to the heart muscles.
In order to be inserted into narrow stenosis the depressurized balloon must be capable of reduction to a minimal thickness around the perfusion catheter; it must also be capable to withstand the high inflating pressures which are required for angioplasty. Hence, the balloon must have walls which are as thin as possible to assure a low profile when depressurized and which are as strong as possible to withstand high pressure.
According to the aforesaid U.S. Pat. No. 4,581,017 the perfusion catheter runs axially through the balloon which is annularly fastened to the catheter by its fore and rear ends. In that environment, the perfusion catheter must be sufficiently stiff to constitute sort of an inner support wall for the balloon to prevent collapse thereof upon inflation in order to give way to the blood flow from beginning to end of the balloon as from the side orifice of the perfusion catheter up to the central outlet thereof. Specifically, it must be sufficiently stiff to withstand the high inflating pressures which are required for angioplasty. However, if the tube has a sufficient diameter to be effective as a perfusion channel, then this requirement results in a considerable wall thickness for the inner catheter, so that the overall minimum diameter of the catheter is increased unfavourably for its use as an interventional instrument for action in narrow stenosis. At the same time, the rigidity of the catheter is increased by this wall thickness of the tube, and it becomes then difficult to place the catheter in tortuous vessels.
As an alternative for the passage of the blood flow through the perfusion catheter during inflation of the balloon, another embodiment provides for having a balloon connected to the outer surface of a tube, the wall of the balloon comprising a pair of longitudinal lobes with portions between the lobes being formed to have thicker walls than the lobes whereby inflation of the balloon causes the lobes to expand radially outward to compress the stenosis while the thicker portions are expected to remain in close proximity to the exterior surface of the tube and provide way for the blood flow past the balloon. In a further alternative for the passage of the blood flow during inflation of the balloon, the balloon is also connected to the outer surface of a tube and is made of a plurality of segments or lobes angularly spaced from each other to allow blood flow upon inflation of the system. In each of these alternatives, if a segmented or lobed balloon fails to achieve the desired result when inflated in a particular angular orientation in the blood vessel, it is necessary to deflate the balloon or balloons, rotate the catheter, and then reinflate the balloon or balloons to complete widening of the stenosis.
Further, when the tubes are designed to be connected to the outer surface of the tube, then it is difficult to accommodate the necessary space for the safe welding or gluing on the surface of a small diameter inner tube.
These problems do not come up with the balloon catheter structures shown in U.S. Pat. Nos. 4,909,252, 5,002,531 and 5,108,370. In these documents, the dilatation balloons have an inflated shape which is toroidal with an elongated longitudinal central aperture or tunnel adapted to allow blood flow during dilatation of the balloon against the stenosis. These balloons are affixed to a catheter by at least one of their walls and the catheter passes inside, or outside, or through the balloon. In the balloons of U.S. Pat. Nos. 4,909,252 and 5,002,531, the inner wall forming the tunnel for blood flow is connected to the outer wall by welding areas or by junction struts regularly spaced apart from each other to avoid deformation of the balloon upon inflation and the resulting reduction of the central tunnel for the blood flow. These areas of junction to the catheter as well as the welding points and junction struts are difficult to manufacture and also constitute solutions of continuity which will generate peak stresses upon inflation of the balloon. The welding points and junction struts also add to the diametral space occupied by the balloon when depressurized. Specifically, the welding points and junction struts have to be sized sufficiently to take up the full inflation pressure required for angioplasty. In absence of such welding points or junction struts as shown in U.S. Pat. No. 5,108,370, the perfusion tunnel through the balloon will collapse under the inflation pressure required for angioplasty, even if the balloon is designed to be relatively short.
In other words, there is a choice of having an internal solid structure inside the balloon to keep the perfusion channel open. This choice sets limits to the diameter of the perfusion channel because the perfusion channel in this case directly determines the minimum deflated diameter of the balloon. Or there is another choice of having a foldable perfusion tunnel that collapses during deflation. This alternative makes struts or similar supporting structures inside the balloon necessary, which are difficult to manufacture, which create peak stresses in the balloon wall and which even when these problems were solved, still would add unfavourably to the diametral space occupied by the balloon when depressurized.
The object of this invention is to seek a substantial reduction of the diametral space occupied by the balloon of an angioplasty perfusion catheter when depressurized for its introduction into a stenosis of a blood vessel, while still providing a large sized perfusion channel for effective blood exchange through the balloon.
To this effect, the angioplasty perfusion catheter according to the invention complies with the definitions given in the claims.
Accordingly, the movable perfusion catheter defining the perfusion channel allows substantial reduction of the diametral space occupied by the balloon of an angioplasty perfusion catheter when depressurized for its introduction into a stenosis of a blood vessel while still allowing a large sized perfusion channel for effective blood exchange through the balloon, because it permits removal of the space consuming perfusion catheter out of the balloon when the latter is deflated. The free flying conduit for the guide wire in the perfusion tunnel allows collapse of the balloon without inducing the guidewire movement but still allows free access to the perfusion tunnel for tubular supporting members guided on the conduit, such as a perfusion catheter. This causes substantial diameter reduction of the depressurized catheter while the perfusion channel size can be increased and selected independently from the size of the depressurized catheter. And a free flying conduit in the perfusion catheter allows passage of a tubular dilator member guided on the conduit to open up the perfusion tunnel for insertion of a perfusion catheter that is considerably larger in size than the conduit.
In that way, the operator may initially only insert into the stenosis the guide wire and its tubular conduit dragging the deflated balloon, while leaving the perfusion catheter in waiting position behind the stenosis, whereby the diametral space occupied by the balloon is minimal for entry into narrow stenosis. As a second step, the operator inflates the balloon in the stenosis for a very short while sufficient to enlarge the stenosis, and immediately thereafter he deflates the balloon to reinstate blood flow through the stenosis. As a third step following deflation of the balloon, the operator may slide the perfusion catheter along the tubular conduit of the guide wire in order to make way into the perfusion tunnel of the deflated balloon. Then, as a fourth step, the operator inflates the balloon to support the vessel wall as long as necessary, the blood flow being assured through the perfusion catheter.
Accordingly, two process phases will be considered, namely:
a first angioplasty phase in which the amount of available pressure to the balloon is of primary importance to break the stenosis, the time during which the pressure is applied being of secondary importance; PA1 a second support phase during which vessel wall flaps that may have been created by the dilatation are secured to the vessel wall; during this phase, time is determining not pressure, because there is no need to have high pressure to put the flaps back to the vessel wall from which they came loose, but there is needed some time until those flaps will connect again to the vessel wall.
In accordance with the invention, this two phase procedure is achieved with a single instrument allowing free diameter choice for the perfusion catheter to ensure good perfusion effect with high volume flow and least risk of blood clogging in narrow channels. The benefit of low pressure in the perfusion phase is then that even when large perfusion diameters are employed, the wall thickness of the perfusion catheter tube can be held within acceptable boundaries. This means that for stenosis with narrow entry openings as frequent in cardiovascular angioplasty, instruments with exceptionally wide perfusion channels can be used. And as a result of the fact that, upon inflation of the balloon for dilatation, its inner wall is allowed to collapse onto the small tubular conduit, and upon inflation of the balloon for vessel wall support, the portion of its wall forming the perfusion tunnel for the perfusion catheter is kept open by the large diameter perfusion catheter, the balloon can have and extremely thin wall with no internal ribs, weldings or struts to achieve the lowest possible profile in deflated condition while withstanding the required pressures.
According to a preferred embodiment of the invention, the balloon forms a hollow cylinder without internal support for its walls and this balloon is closed by welding it inside wall to inside wall at its proximal end, so that the welding places of the balloon may also stay outside the stenosis. And within this frame, to get rid of any welding points and peak stresses at the distal end of the balloon, and thereby achieve the narrowest diameter at that place, the balloon may be linked to the tubular conduit by a net affixed to the distal end of the tubular conduit, which net extends all the way around and along the balloon to be welded to the proximal end thereof.
The invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, a preferred embodiment and variant of the invention.